The present invention relates to valve and filter mechanisms useful in machinery that employs a hydraulic circuit. More specifically, the invention provides an orifice element with an integrated filter. The orifice element is useful for throttling a flow rate of hydraulic oil in one direction in a hydraulic circuit. The hydraulic circuit may be used, for example, in a hydraulic drive unit for independently applying a driving force generated by hydraulic pressure to a driven body. A slow return valve in the hydraulic circuit regulates the flow rate of hydraulic oil flowing out of a hydraulic actuator that generates the driving force for a hydraulic drive unit that uses the hydraulic circuit.
A hydraulic drive unit that conveniently provides a driving force created by oil pressure without the need to lay hydraulic pipes if only an electric power source is present has been used, for example, to drive and lift a working element in an agricultural vehicle with respect to cultivated ground. Such drive units are expected to see continued and wider application in this and other fields.